JP3369399B2 - Fabrication method of refractive index multidimensional periodic structure - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a refractive index multi-dimensional periodic structure, which can be expected to be applied to the manufacture of semiconductor optical devices.

[0002]

2. Description of the Related Art A structure in which two regions having different refractive indices are alternately arranged and at least in two-dimensional directions with a certain period can be said to be a refractive index multidimensional periodic structure. This structure is, for example, a semiconductor laser with a quantum efficiency of 100%,
It is considered to have the possibility of realizing a useful optical element (for example, Document I: "Applied Physics" Vol. 63, No. 6, pp. 604-).
607 (1994)). Among the refractive index multi-dimensional periodic structures, as a conventional method for producing a refractive index two-dimensional periodic structure, for example, reference II (Applied Physics Letters vol.64, pp.687-689)
(1994)). This forms a resist pattern having a circular opening periodically on the surface of a semiconductor substrate, and then etches the portion of the substrate not covered with the resist by etching means such as reactive ion etching technique. The method is to form a cylindrical hole in each predetermined portion of the substrate. In the structure obtained by this method, the cylindrical hole portion is air (low refractive index portion), and the other portion is the substrate (high refractive index portion), so the refractive index two-dimensional periodic structure is formed by both. To be done. Further, as a conventional method for producing a three-dimensional refractive index periodic structure, for example, reference III (Physical Review Letters vol.67, pp.2295
-2298 (1993)). This is done by drilling a cylindrical hole from the surface of the dielectric substrate to the substrate and
It is a method of forming each in the direction. In the structure obtained by this method, the cylindrical hole part is air (low refractive index part), and the other part is the substrate (high refractive index part), so the refractive index three-dimensional periodic structure is formed by both. To be done.

[0003]

[Problems to be Solved by the Invention] However, Document II
In the case of the conventional method disclosed in, it is difficult to make a deep hole because a cylindrical hole is formed by dry etching. Therefore, it is difficult to manufacture a two-dimensional periodic structure with a large refractive index.

In the case of the conventional method disclosed in Document III, FIG. In the case of using reactive ion etching as described in the description of No. 2, it is difficult to make a deep hole as in the case of Document II, so that it is difficult to fabricate a thick refractive index three-dimensional periodic structure. There is a problem. Further, since it is necessary to carry out reactive ion etching three times for making holes in three directions, it is considered that the yield and reproducibility at the time of producing the target refractive index three-dimensional periodic structure will be extremely poor. . Further, in the case of the conventional method disclosed in Document III, FIG. When a mechanical drill is used as described in the description of item 2, there arises a problem that a dielectric substrate such as a compound semiconductor substrate having poor mechanical strength cannot be used.

A refractive index multidimensional periodic structure having a desired thickness can be easily manufactured, and even when a compound semiconductor material which is a typical material for manufacturing an optical element is used, the desired refractive index multidimensional periodic structure is obtained. It is desired to realize a method capable of easily producing a structure.

[0006]

Therefore, according to the method for producing a refractive index multidimensional periodic structure of the present invention, an underlayer having a periodic concavo-convex structure on its surface is prepared, and on the surface of the underlayer, Two kinds of thin films whose refractive index is changed by at least one of them are alternately and each of the film thicknesses are equal to or substantially equal to the step in the unevenness (hereinafter, also referred to as “predetermined film thickness”). The above-mentioned post-treatment is performed on the laminated sample. In the present invention, the two kinds of thin films may have different refractive indexes from the beginning, and the refractive index of at least one of the thin films may be further changed by post-treatment, or both of the two kinds of thin films may be initially changed. The refractive index may be the same, but the refractive index of at least one of the thin films may change after the post-treatment. In the later embodiment, the two types of thin films formed on the base have different refractive indexes from the beginning, and one of them further changes in post-treatment (specifically, in oxidation treatment). Here is an example:

According to the present invention, on a predetermined base surface,
Two kinds of thin films whose refractive indexes are changed by post-treatment are laminated alternately and each of them has a predetermined thickness, and the post-treatment is performed on the laminated sample. Since it is done, 2 in the direction perpendicular to the base surface
A structure is formed in which two kinds of thin films are alternately laminated with almost the same film thickness, and two kinds of thin films appear alternately along a direction parallel to the base surface. Here, when the concave-convex structure on the base surface is along one direction parallel to the base surface, a refractive index two structure consisting of a refractive index periodic structure along this direction and a refractive index periodic structure along the direction perpendicular to the base surface is used. A dimensional periodic structure is obtained. Further, in the case where the uneven structure of the underlying surface is along two directions parallel to the underlying surface, a refractive index tertiary structure composed of a refractive index periodic structure along these two directions and a refractive index periodic structure along the direction perpendicular to the underlying surface. The original periodic structure is obtained. Then, the periods of the two types of thin films in the direction perpendicular to the base surface can be controlled by the size of the step in the concavo-convex structure formed on the base surface, while the appearance periods of the two types of thin films in the direction parallel to the base surface are:
Since it can be controlled by one or both of the width of the concave portion and the width of the convex portion in the concavo-convex structure formed on the underlying surface, the control of the refractive index periodic structure can be easily performed. The period in the refractive index periodic structure may be any period according to the purpose of use of the structure. For example, in the case of manufacturing the photonic bandgap structure shown in Document I,
The period referred to in the present invention is set to a dimension approximately the same as the wavelength of light to be handled. In this case, realization of an optical device capable of artificially controlling spontaneous emission light can be expected.

In the present invention, the underlying constituent material and the constituent materials of each of the two types of thin films may be arbitrary materials depending on the use of the refractive index multidimensional periodic structure. Typically, at least two types of thin films should be compound semiconductor materials. This is because it suits the application of the optical element. Further, it is preferable that the two kinds of thin films are made of a material that allows good crystal growth, for example, those having close lattice constants. This is because a refractive index multidimensional periodic structure with excellent quality can be obtained. The underlayer is also preferably made of the same material as one of the constituent materials of one of the two types of thin films, or is made of a different material that allows good crystal growth of the thin film. This is because the quality of the two types of thin films formed on the base becomes better, and a good refractive index multidimensional periodic structure can be obtained. Also, the base is 2
If a base made of the same material as one of the two types of thin films is used and stacking is started from the other thin film of the two types of thin films on this base, the convex portion of the base surface itself has a refractive index periodic structure. It will form a part.

[0009]

Further, according to the present invention, the first thin film which is etched by the etching method to be performed later and the first thin film which is not etched or is substantially etched by the etching method is formed on the base on which the periodic uneven structure is formed. Alternatively, the second thin film that is not formed may be alternately laminated to have a predetermined film thickness, and the sample that has been laminated may be subjected to the etching.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a method for producing a refractive index multidimensional periodic structure of the present invention will be described below with reference to the drawings. However, the drawings used in the description are merely schematic representations so that the present invention can be understood. Further, in each drawing, the same constituent components are denoted by the same reference numerals, and the duplicated description thereof may be omitted. Further, although details will be described later, in each figure, in order to distinguish the GaAs thin film from the AlAs thin film, the AlAs thin film itself or an oxide film (FIG. 5 (B)) and holes (FIG. 7 (B)) related thereto are formed. Is shown with a halftone dot pattern.

1. Description of Example of Fabrication of Two-Dimensional Refractive Index Periodic Structure First, a GaAs thin film is used as a base, and a GaAs substrate in which a concavo-convex structure is repeated in one direction parallel to the substrate surface and two types of thin films having different refractive indices are used. And Al
An example of producing a two-dimensional refractive index periodic structure using an As thin film will be described. FIG. 1 and FIG. 2 are process diagrams used for the explanation, and are process diagrams showing perspective views of the state of the sample in the main steps of the manufacturing process. In this example using GaAs and AlAs, the refractive index of GaAs is about 3.5 and the refractive index of AlAs is about 2.9, so that the GaAs thin film has a high refractive index thin film and the AlAs thin film has a low refractive index. Hit each thin film.

First, the ridge-shaped convex portions 11a are formed on the surface of the GaAs substrate so as to be juxtaposed along the width direction (direction indicated by Y in FIG. 1A) at a period P.
s The substrate surface is processed by using ordinary photolithography technology and etching technology. This processed GaAs
The substrate 11 had on its surface a periodic structure (one-dimensional periodic structure) 11x in which convex portions 11a and concave portions 11b were repeated along one direction parallel to the substrate surface (Y direction in FIG. 1A). GaAs substrate 11, that is, base 11 in the present invention
(FIG. 1 (A)). Here, the width W1 of the convex portion 11a,
The values of the width W2 of the concave portion 11b and the step H in the unevenness depend on the structure of the refractive index periodic structure.
It can be any value. Specifically, W1 and W2 can be determined according to how the period P (see FIG. 1A) in the periodic structure 11x is set, and H is Ga.
The period Pz (see FIG. 1B) of the periodic structure formed later in the direction perpendicular to the surface of the As substrate 11 can be determined according to what period. For example W1 = W
If 2 = H, the refractive index periodic structure in the direction parallel to the surface of the GaAs substrate 11 and the refractive index periodic structure in the direction perpendicular to the surface of the GaAs substrate 11 have the same period. It becomes possible to fabricate a periodic structure. In addition, the convex portion 11a
The side wall (the side wall of the recess 11b) should be as vertical as possible to the surface of the GaAs substrate. This is because the concavo-convex structure is likely to be favorably stored even after the thin film is formed on the underlayer 11.

In this way, GaA having a concavo-convex structure on its surface
The AlAs thin film 13 as the first thin film on the s substrate 11
And the GaAs thin film 15 as the second thin film are alternately laminated so that the respective film thicknesses thereof are equal to or substantially equal to the step H in the unevenness (FIG. 1).
(B), FIG. 2 (A)). The number of laminations of these thin films 13 and 15 is such that a refractive index periodic structure having a desired thickness can be manufactured. As a film forming method for these thin films 13 and 15, a film forming method for easily transferring the uneven structure 11x of the underlayer 11 is preferable. For example, the molecular beam growth method (MBE method) is mentioned as one of preferable film forming methods.

In the process of forming the thin films 13 and 15, Al
Each of the As thin film 13 and the GaAs thin film 15 grows in a state in which the growing portion on the concave portion 11b and the growing portion on the convex portion 11a are deviated by the step height H of the unevenness. Therefore, in the sample which has been subjected to the alternate lamination, the structure in which the GaAs thin films and the AlAs thin films are alternately and periodically present both in the direction parallel to the surface of the GaAs substrate 11 and along the unevenness and in the direction perpendicular to the surface of the substrate 11 Thus, the two-dimensional refractive index periodic structure 17 can be manufactured (FIG. 2 (B)).

2. Description of Fabrication Example of Three-Dimensional Refractive Index Periodic Structure Next, as a base, a GaAs substrate having a concavo-convex structure repeated in two directions parallel to the substrate surface is used, and two types of thin films having different refractive indices are used. Thin film and Al
An example of producing a three-dimensional refractive index periodic structure using an As thin film will be described. FIG. 3 and FIG. 4 are process diagrams used for the explanation, and are process diagrams showing perspective views of the state of the sample in the main steps of the manufacturing process. It should be noted that the two directions parallel to the substrate surface mentioned here are directions excluding the case where they are opposite to each other by 180 °. Here, an example in which the two directions are two directions orthogonal to each other (each direction indicated by X and Y in FIG. 3A) will be described.

First, the convex portion 2 is formed on the surface of the GaAs substrate.
The surface of the GaAs substrate is processed by the usual photolithography technique and etching technique so that the 1a and the recess 21b are alternately formed in each of two directions parallel to the substrate surface. Specifically, the recess 2 having a square or rectangular planar shape at the opening and a depth (step) of H
1b is formed on the GaAs substrate in large numbers, and
The GaAs substrate is processed so that the recesses 21b are staggered and the four corners are in contact with the corners of the other recesses 21b. This processed GaAs substrate 21 is
Convex portions 21a are formed along each of two directions parallel to the substrate surface.
Further, the GaAs substrate 21 has a periodic structure (two-dimensional periodic structure) 21x in which the concave portions 21b are repeated, that is, the base 21 in the present invention (FIG. 3 (A)). In addition, here, the size and shape of the top surface of the convex portion 21a and the size and shape of the opening portion of the concave portion 21b are the same. That is, the dimension of the top surface of the convex portion 21a in the X direction and the dimension of the opening portion of the concave portion 21b in the X direction are both Wx, and the dimension of the top surface of the convex portion 21a in the Y direction and the opening portion of the concave portion 21b. And the dimension in the Y direction at
Both are Wy. Further, the respective values of Wx, Wy, and H can be set to arbitrary values according to the structure of the refractive index periodic structure. Specifically Wx and W
y can be determined according to the respective periods Px and Py in the X direction (see FIG. 3A) in the periodic structure 21x, and H is the GaAs substrate 11
Can be determined according to what the period Pz (see FIG. 3B) of the periodic structure formed later in the direction perpendicular to the surface of is. For example, if Wx = Wy = H, a refractive index periodic structure in each of two directions parallel to the surface of the GaAs substrate 11, that is, a refractive index periodic structure in the X direction,
It is possible to manufacture a three-dimensional refractive index structure in which the refractive index periodic structure in the Y direction and the refractive index periodic structure in the direction perpendicular to the surface of the GaAs substrate 11 have the same period. Also, the convex portion 2
The side wall of 1a (the side wall of the recess 21b) is made of GaAs as much as possible.
It is good to make it perpendicular to the substrate surface. This is because the uneven structure is likely to be favorably stored even after the thin film is formed on the base 21.

In this way, GaA having a concavo-convex structure on its surface
On the s substrate 21, AlAs thin film 13 and GaAs thin film 1
5 and 5 are laminated alternately so that the respective film thicknesses are equal to or substantially equal to the step H (FIG. 3B).
FIG. 4 (A)). The number of laminations of these thin films 13 and 15 is such that a refractive index periodic structure having a desired thickness can be manufactured. The method of forming these thin films 13 and 15 uses the uneven structure 2 of the base 21.
A film forming method in which 1x is easily transferred is preferable. For example, the molecular beam growth method (MBE method) is mentioned as one of preferable film forming methods.

In the process of forming the thin films 13 and 15, Al
Each of the As thin film 13 and the GaAs thin film 15 grows in a state in which the growing portion in the concave portion 21b and the growing portion on the convex portion 21a are deviated by the step difference of the concave and convex portions. Therefore, in the sample that has been subjected to the alternate lamination, the substrate 2 is also formed in each of the two directions (X and Y directions) parallel to the surface of the GaAs substrate 21.
GaAs thin film and AlA even in the direction perpendicular to the surface.
Since a structure in which s thin films are present alternately and periodically is produced, the refractive index three-dimensional periodic structure 23 can be produced (FIG. 4).
(B)).

3. First Embodiment Next, two kinds of thin films having different refractive indexes by post-treatment are alternately laminated with a predetermined film thickness on a base having a periodic uneven structure on the surface, and The invention that performs the post-processing will be described. However, here, an example will be described in which this technical idea is further applied to the method described in the manufacturing example of the refractive index two-dimensional periodic structure. In the fabrication example of the above-mentioned two-dimensional periodic structure of refractive index, AlAs is formed on a predetermined GaAs underlayer 11.
An example in which the thin film 13 and the GaAs thin film 15 are alternately laminated to form a desired refractive index multidimensional periodic structure has been described. In this case, since the refractive index of GaAs is about 3.5 and the refractive index of AlAs is about 2.9, a refractive index multidimensional periodic structure with a refractive index difference of about 0.6 can be obtained. However, if a refractive index multidimensional periodic structure having a larger refractive index difference can be manufactured, a refractive index multidimensional periodic structure for such an application can be easily manufactured, which is preferable. Therefore, in the first embodiment, the following procedure is taken. This description will be described mainly with reference to FIG.

First, the refractive index two-dimensional periodic structure 17 is created by the procedure described in the manufacturing example of the refractive index two-dimensional periodic structure (FIG. 5A). Next, the refractive index two-dimensional periodic structure 17
Appropriate processing is performed on this two-dimensional periodic structure of refractive index so that a part of each layer of AlAs in the inside is exposed to the outside. This processing can be performed by cleavage, for example. Of course, if a part of each AlAs layer is already exposed to the outside, this processing is unnecessary.

Next, the sample is placed in an atmosphere that promotes oxidation such as a water vapor atmosphere and has a high temperature (for example, a temperature of about 400 ° C.) for several hours. In this process, each GaAs thin film 15 does not change, but each AlAs thin film 13 is oxidized to be an oxide film 13x having a refractive index of about 1.5 (FIG. 5 (B)). Therefore, the refractive index two-dimensional periodic structure 17x composed of GaAs (both the substrate 11 and the GaAs thin film 15) and the oxide film 13x can be manufactured. In the case of this structure, since the refractive index of GaAs is about 3.5 and the refractive index of the oxide film 13x is about 1.5, a two-dimensional periodic structure with a refractive index difference of about 2.0 is obtained. Therefore, a refractive index two-dimensional periodic structure having a larger difference in refractive index than in the case of manufacturing the refractive index two-dimensional periodic structure is obtained. For details of the above thermal oxidation process, see, for example, Document IV (Applied Physics Lett).
ers (Available Physics Letters), 1990, Vol.57, pp.2844 ~ 28
46).

In the above description, an example of oxidizing the refractive index two-dimensional periodic structure has been described.
It is considered possible to convert the AlAs thin film 13 into an oxide film by subjecting the refractive index three-dimensional periodic structure shown in FIG. However, in that case, as shown in FIG. 6, the AlAs thin film 13 is two-dimensionally connected by intentionally making the film thickness D of the AlAs thin film 13 which is an oxidized film slightly thicker than the step H in the unevenness. Leave it in a state. However, AlAs
The thickness t of the portion of the thin film that is thicker than the step H
Must have a film thickness that can be optically ignored.
For example, if the step H is 0.5 μm, the film thickness t is considered to be about several hundred Å at most. Therefore, AlA
It is considered that the film thickness D of the s thin film should be at least 0.5 μm + several hundred Å. By doing so, it is considered that the AlAs thin film 13 can be oxidized by the subsequent oxidation treatment even in the case of the refractive index three-dimensional periodic structure.

Further, in the first embodiment,
Although the first thin film and the second thin film have different refractive indexes from the beginning, the first and second thin films have the same refractive index until after the post-treatment, and the post-treatment has the same refractive index. The present invention also includes a configuration in which the refractive index of at least one of the thin films changes.

4. Second Embodiment Next, a first thin film that is etched by an etching method that will be performed later and a film that is not or is not substantially etched by the etching method on a base on which a periodic uneven structure is formed on the surface. An invention will be described in which the second thin film that is not formed is alternately laminated to have a predetermined film thickness, and the etching is performed on this sample. This explanation will be given mainly with reference to FIG. 7.

First, the refractive index two-dimensional periodic structure 17 is created by the procedure described in the manufacturing example of the refractive index two-dimensional periodic structure (FIG. 7A). Next, the refractive index two-dimensional periodic structure 17
Appropriate processing is performed on this two-dimensional periodic structure of refractive index so that a part of each layer of AlAs in the inside is exposed to the outside. This processing can be performed by cleavage, for example. Of course, if a part of each AlAs layer is already exposed to the outside, this processing is unnecessary.

Next, this sample is etched by an etching method which dissolves AlAs but does not dissolve GaAs (including the case where it does not substantially dissolve). This can be done, for example, by immersing the sample in hydrofluoric acid. In this process, since each AlAs thin film 13 is removed from its exposed portion, the portion of the sample where the AlAs thin film was present finally becomes the void 31 (FIG. 7 (B)). Therefore, G
A refractive index two-dimensional periodic structure 17y composed of aAs (both substrate 11 and GaAs thin film 15) and holes 31 can be produced. In the case of this structure, the refractive index of GaAs is about 3.
5. Since the refractive index of the holes is about 1, the difference in refractive index is about 2.
A two-dimensional periodic structure with a refractive index of 5 is obtained. In the second embodiment, a refractive index two-dimensional periodic structure having a larger difference in refractive index than the manufacturing examples of the refractive index two-dimensional periodic structure and the first embodiment can be obtained.

In the above, some embodiments of the present invention have been described. However, the present invention is not limited to the above embodiment.

For example, in each of the above-described fabrication examples of the two-dimensional periodic structure of refractive index and the three-dimensional periodic structure of refractive index, a base is a GaAs substrate and two kinds of thin films having different refractive indices are made of Al.
The example using the As thin film and the GaAs thin film has been described. Further, in the first embodiment, an example has been described in which the underlayer is a GaAs substrate, and two types of thin films whose refractive index changes by post-treatment are AlAs thin films and GaAs thin films. Further, in the second embodiment, an example has been described in which the underlayer is a GaAs substrate, and the thin film that is etched by a later etching method and the thin film that is not etched are AlAs thin films and GaAs thin films. However, these materials can be replaced with other suitable materials that can achieve the objects of this invention. For example, in the first embodiment, two types of thin films having different refractive indexes are AlAs thin film and AlGaAs thin film,
It is considered that the same effect as that of the first embodiment can be obtained when two types of AlGaAs thin films having different compositions are used. In that case, both are oxidized, but the degree is different, so it is considered that the refractive index periodic structure is secured.

Further, in the above embodiment, in the example of manufacturing the three-dimensional refractive index structure, two directions parallel to the substrate surface are orthogonal to each other (X in FIG. 3A,
(Each direction indicated by Y). However, the two directions do not have to be orthogonal to each other, and may be directions that form an acute angle or an obtuse angle with each other. In that case, the convex portion 21
It is only necessary to take measures such as making the planar shape of the a and the concave portion 21b into a parallelogram shape.

[0031]

As is apparent from the above description, according to the method of manufacturing a refractive index multi-dimensional periodic structure of the present invention, an underlayer having a periodic uneven structure is prepared, and the surface of the underlayer is prepared. Two kinds of thin films whose refractive index is changed by post-treatment are alternately laminated on each other so that the respective film thicknesses are equal to or substantially equal to the step in the unevenness, The post-treatment is performed on the laminated sample. In the case of this method, dry etching may be used when forming a base having a concavo-convex structure, but the etching depth may be shallow. After that, it is only necessary to alternately stack two types of thin films with a predetermined film thickness and change the refractive index by post-treatment. Therefore,
A refractive index multi-dimensional periodic structure having a desired thickness can be easily manufactured, and even when a compound semiconductor material, which is a typical material for manufacturing an optical element, is used, a desired refractive index multi-dimensional periodic structure can be easily manufactured. Can be made. In addition, a refractive index multidimensional periodic structure can be manufactured with higher reliability and higher reproducibility than ever before.

[Brief description of drawings]

FIG. 1 is an explanatory view (No. 1) of a production example of a two-dimensional periodic structure of refractive index.

FIG. 2 is an explanatory view (No. 2) of an example of manufacturing a two-dimensional periodic structure of refractive index.

FIG. 3 is an explanatory view (No. 1) of an example of manufacturing a three-dimensional refractive index periodic structure.

FIG. 4 is an explanatory view (No. 2) of an example of manufacturing a three-dimensional periodic structure of refractive index.

FIG. 5 is an explanatory diagram of the first embodiment.

FIG. 6 is an explanatory diagram of another example of the first embodiment.

FIG. 7 is an explanatory diagram of the second embodiment.

[Explanation of symbols]

11: Base (GaAs substrate) having a one-dimensional periodic structure 11a: convex portion (ridge-shaped convex portion) 11b: concave portion 13: First thin film (AlAs thin film) 13x: oxide film (a film obtained by oxidizing AlAs) 15: Second thin film (GaAs thin film) 17, 17x, 17y: Two-dimensional periodic structure of refractive index 21: Base having a two-dimensional periodic structure 21a: convex portion (for example, cubic convex portion) 21b: concave portion (for example, a cubic concave portion) 23: Refractive index three-dimensional periodic structure 31: Hole

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-4-180283 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 5/18

Claims (6)

(57) [Claims] 1. A base having a periodic concavo-convex structure on its surface is prepared, and two kinds of thin films whose refractive index is changed by post-treatment are alternately and alternately formed on the surface of the base. Laminates are formed so that the respective film thicknesses are equal to or substantially the same as the step difference in the unevenness, and the post-treatment is performed on the laminated sample, and the post-treatment is performed. Manufacturing method. 2. A base having a periodic concavo-convex structure formed on the surface thereof is prepared, and a first thin film oxidized on the surface of the base by an oxidation treatment performed later is compared with the first thin film. Second thin films that are less oxidized or are not substantially oxidized are laminated alternately and so that their respective film thicknesses are equal to or substantially equal to the step difference in the unevenness. A method for producing a refractive index multi-dimensional periodic structure, which comprises subjecting a sample to the oxidation treatment. 3. The method for producing a refractive index multidimensional periodic structure according to claim 1, wherein the periodic uneven structure is provided as the base along one direction parallel to the surface of the base. A method of manufacturing a refractive index multi-dimensional periodic structure, which comprises manufacturing a refractive index two-dimensional periodic structure using a repeating base. 4. The method of manufacturing a refractive index multi-dimensional periodic structure according to claim 1, wherein the base has the periodic concavo-convex structure along two directions parallel to the surface of the base. A method for producing a refractive index multi-dimensional periodic structure, which is characterized in that a three-dimensional periodic structure of refractive index is produced using an underlayer which is repeated (however, when the two directions are opposite to each other by 180 °, except.). 5. A base having a periodic concavo-convex structure formed on the surface thereof, wherein the concavo-convex structure is repeated along one direction parallel to the surface of the base, is prepared. First thin films that are etched by an etching method to be performed later and second thin films that are not or not substantially etched by the etching method are alternately and each have a film thickness equal to the step in the unevenness. Or a method of manufacturing a refractive index multi-dimensional periodic structure, which comprises laminating so that the film thicknesses are substantially equal and performing the etching on the laminated sample. 6. The method for manufacturing a refractive index multi-dimensional periodic structure according to claim 1, wherein the width of the concave portion, the width of the convex portion, and the unevenness in the direction in which the unevenness of the uneven structure is repeated. A method for producing a refractive index multi-dimensional periodic structure, characterized in that the period of each dimension in the refractive index multi-dimensional periodic structure is controlled by controlling each dimension of the step in.